Technical Field
The present disclosure relates to physical quantity measuring systems that detect physical quantities of a measurement target portion by using a principle that the resonant frequency of a resonator varies depending on a physical quantity such as the temperature and the magnetic field strength, and to physical quantity measuring devices to be used in such physical quantity measuring systems.
Background Art
Conventionally, a variety of systems for wirelessly detecting physical quantities of a remotely located measurement target portion have been devised. A wireless temperature measuring system that measures the temperature of a remote location is one such system. As described in Patent Document 1, for example, a wireless temperature measuring system is constituted by a sensor device disposed in a temperature measuring unit and a temperature measuring device disposed at a position spaced apart from the sensor device. The sensor device and the temperature measuring device are configured to be capable of wirelessly communicating with each other.
Among such wireless temperature measuring systems, there is a wireless temperature measuring system that includes a sensor device constituted by a sensor-side antenna and a resonator. In this case, a temperature measuring device transmits an excitation signal to the resonator of the sensor device. The resonator has temperature characteristics affecting its resonant frequency and thus generates a resonance reverberation signal at a resonant frequency corresponding to the temperature of a temperature measurement target portion on which the resonator is disposed. The resonance reverberation signal is transmitted to the temperature measuring device via the sensor-side antenna.
The temperature measuring device detects the frequency of the received resonance reverberation signal and thus calculates the temperature detected by the resonator.
The resonant frequency changes not only with a change in the temperature but also with a change in other physical quantities, such as the magnetic field strength, and thus it is possible to measure other physical quantities of the measurement target portion, as well as on the basis of a change in the resonant frequency.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 3-238594